Billing in a Packet Data Network

1. A method for charging for a user's terminal's accessing of a packet data network, the method comprising: forming a data link between the terminal and the packet data network; receiving from the terminal a user identity suitable to identify the terminal to an external telecommunications network; generating billing data based on the user identity; sending the billing data to an accounting server of the external telecommunications network; generating a billing code corresponding to the price of accessing the packet data network; generating a cryptographic checksum using at least the billing code; and using the cryptographic checksum in a billing set up to verify that the user is provided with the correct price and that the user has accepted the access for that correct price.

2. A method according to claim 1 further comprising providing the terminal with access to a subscriber identity module having the user identity.

3. A method according to claim 1 further comprising authenticating the terminal using the subscriber identity module.

4. A method according to claim 1 , wherein the packet data network is a public wireless internet protocol access network.

5. A method according to claim 1 , wherein the data link is formed directly between the terminal and the packet data network.

6. A non-transitory computer readable medium encoded with a computer program for controlling a packet data network accessible to at least one user's terminal, comprising: computer program code for causing the network to form a data link between the terminal and the packet data network; computer program code for causing the network to receive from the terminal a user identity suitable to identify the terminal to an external telecommunications network; computer program code for causing the network to generate billing data based on the user identity; computer program code for causing the network to send the billing data to an accounting server of an external telecommunications network; computer program code for causing the network to generate a billing code corresponding to the price of accessing the packet data network; computer program code for causing the network to generate a cryptographic checksum using at least the billing code; and computer program code for causing the network to use the cryptographic checksum in billing set up to verify that the user is provided with the correct price and that the user has accepted the access for that correct price.

7. A non-transitory computer readable medium according to claim 6 , further comprising computer program code for causing the network to authenticate the terminal using the subscriber identity module.

8. A non-transitory computer readable medium according to claim 6 , wherein the packet data network is a public wireless internet protocol access network.

9. A non-transitory computer readable medium according to claim 6 , wherein the data link is formed directly between the terminal and the packet data network.

10. A method in a mobile terminal for charging of accessing a packet data network, the terminal being related to a subscriber identity module and the method comprising: sending a terminal originated authentication starting request containing a network access identifier having an international mobile subscriber identifier, the terminal originated authentication starting request further containing a protection code; receiving from the packet data network an authentication start response message containing one or more challenges corresponding to as many session keys and signed responses, the protection code, a billing information code, a session identity and a billing information computed for the billing information code, and a message authentication code calculated using: a hash function; the one or more challenges; and corresponding session keys; testing with the message authentication code that the parameters carried by the authentication start response message indeed originate from a GSM telecommunications network to which the subscriber identity module is related; handling the billing information received from the packet data network; generating a reply message authentication code based on the corresponding signed responses to be used for responding to the packet data network; generating a shared secret for use with the packet data network, wherein the generating of the shared secret uses at least the session keys; generating and sending to the packet data network a reply message containing an indication whether the user accepted the billing for the service, the reply message authentication code, the message authentication code of the billing code, and the protection code; and receiving from the packet data network an authentication answer message containing a message authenticator and informing the user of a start of billing if the message authenticator contained by the authentication answer message is correct.

11. A method according to claim 10 , wherein the handling comprises a sub-step of providing a user or the mobile terminal with an information of the price of the service requested by the user.